Wednesday, October 31, 2012

Six Days Of Sandy

Much has been or will be written about Hurricane/Superstorm Sandy.  The impacts are still being assessed and it may be weeks before we have the full picture.  It was an historic and unprecedented storm.  NASA has put together a wonderful video of Sandy from its development as a tropical depression to its transformation to a superstorm and finally a weaker system.  The time period covered here is from October 23 to 31.

However, an even better video covering the period October 25 to 31 was produced by NOAA NESDIS.  These rapid scan images were produced into a time-lapse movie as an experiment using the GOES-14 image.  The images are using visible light with a one kilometer resolution.

Movie credit: NOAA/CIMSS at the University of Wisconsin-Madison.

Sandy is too large a storm to be viewed entirely at this resolution.  The view is centered on the central core and extends out a few hundred miles.  It begins in the central Bahamas as a hurricane and transforms north of the Bahamas as a hybrid storm.  Finally, Sandy makes a transition to extratropical just before making landfall on October 29th.

This is a fascinating view of the storm.  I hope you will appreciate the power being generated by Sandy.  You can see the tops of thunderstorms bubbling up through the cirrus overcast.  Sandy generated a tropical storm force wind field that was up to 1000 miles across at times.  The central pressure was so low that if it had been a pure hurricane it would have been a category 4 storm.  However, the transition to a hybrid spread the winds over a much larger area preventing Sandy from concentrating the winds near the center.


Monday, October 29, 2012

Sandy Update: Monday

Update: 10 p.m. EDT

Sandy made landfall about 5 miles southwest of Atlantic City, New Jersey around 8 p.m. EDT.  It came ashore as an extratropical cyclone as Sandy made a quick transition during the late afternoon.  The storm still had sustained winds up to 80 mph and was moving west-northwest at 21 mph.  Sandy slowed as it moved inland and may slow some more over the next few hours.

The windfield around Sandy as of 9 p.m. EDT, October 29, 2012.  Click on the image for a larger view.  Image Credit: NOAA.
Notice the area colored in yellow.  These are winds in the range of 45 to 60 mph.  This is a very large area of high winds and it is pushing water into New York harbor due to the southeast winds.  It produced a record flood for lower Manhattan.

Sandy continues to move inland and was near Wilmington, Delaware as of 10 p.m. EDT.  Inland winds of 40 to 50 mph were common.  This heaviest rains were now south and west of the center.

The radar from Dover AFB as of 10 p.m. EDT, October 29, 2012.  Sandy was centered southwest of Wilmington, Delaware.  Image Credit: WLTX-TV.
Heavy snows are now falling in West Virginia and western Virginia.  The snow extends south into the mountains of North Carolina, but amounts have been generally light so far.  More snow is expected overnight and through the day on Tuesday.

Update: 6 p.m. EDT

Sandy is now extratropical.  However, that does not alter the overall pattern of the storm.  It has been making rapid transition during the past few hours.  The 5 p.m. analysis of the wind field is below with the radar composite from 5:48 p.m.  The storm is approaching Cape May, New Jersey and should make landfall in about an hour.

The wind field over the radar.  Click on the image for a larger view.  The storm is extratropical.  Image Credit: NOAA.

Update: 2 p.m. EDT

Hurricane Sandy is accelerating and turning to the west-northwest.  The storm has been moving northwest over the past three hours, but it is clearly turning.  Forward motion is now 28 mph and central pressure is 940 mb (27.76 in.).  Maximum sustained winds still at 90 mph, but it appears that an area of strongest winds are developing north of the center.

Windfall analysis as of 1 p.m. EDT October 29, 2012.  Image Credit: NOAA.
Radar image of Sandy as of 2 p.m. EDT October 29, 2012.  Image Credit: WLTX-TV.
The faster forward motion means that the center will cross the coast earlier than forecast.  In addition, it could move faster as it is affected by a strongly negatively tilted trough shown in this mornings upper-air analysis.  The jet stream may cause a further deepening of the pressure.

Analysis of the 250 mb level showing strong winds along the East Coast.  Image Credit: NCAR/RAP.

Saturday, October 27, 2012

The Dance Begins

The upper-level trough that has been moving through the central part of the U.S. is beginning to affect Hurricane Sandy.  It is moving east and energy will be moving into the base of the trough that will cause to tilt negatively.  Initially this will push the hurricane to the northeast.  However, as the trough gets close and the upper-level winds back, Sandy will turn north and then westward moving inland in the Northeast.

The 500 mb analysis for Friday evening October 26, 2012.  Click on the image for a larger view.  Image Credit: WSI.

Wind shear has been increasing over the hurricane and it is beginning to resemble a hybrid system.  A warm core typical of the tropical cyclone is in place, but the center does not have a ring of thunderstorms surrounding it.  NASA imagery showed the thunderstorms displaced to the north Friday evening.

Friday, October 26, 2012

The Perfect Storm 2

In the previous post, which was written on Sunday, I described a scenario that would play out over the next 7 to 10 days.  The details often change significantly at those time frames.  However, the computer models have done a reasonably good job at the overall weather pattern.  The model which has performed the best in my opinion has been the European model at the medium-range.  Now most of the models are clustered toward a similar solution, although the American model (GFS) continues to show some strange results.

The overall pattern is a negatively tilted trough pushing into the eastern part of the country and picking up the northward moving hurricane.  As the two interact Sandy will transform from a tropical cyclone to a nor’easter.  The wind will greatly expand and the storm may become a monster worthy of a Halloween trick.  Sandy will weaken as a hurricane, but may strengthen as a nor’easter before moving into Northeast.

The 500mb forecast pattern by the ECMWF model.  The top chart is for Sunday evening while the bottom chart is for Tuesday morning.  Click on the image for a larger view.  Image Credit: WSI.

Sunday, October 21, 2012

Coastal Storm Followed By Cold Weather?

The South Carolina State Fair was lucky and enjoyed great weather for its entire run which ended today.  Dry weather is expected to continue over the Midlands most of the coming week and it will be delightful fall weather.  However, the weather pattern will begin changing this week and the Midlands, as well as much of the East coast, will be challenged by the changing conditions next weekend.

All of the computer models, used for medium-range weather forecasts, are converging on a solution that changes the weather for much of North America.  The change is already underway.  It is happening in the middle troposphere (500 mb) over western Canada where a double-barrel low pressure system is pushing the polar jet stream south from Alaska to California.

The 500 mb chart for 00z, 22 Oct 2012.  Winds generally blow parallel to the contours lines.  Click on the image for a larger view.  Image Credit: WSI.

This will bring colder air south into the western U.S.  The low pressure system will slowly swing east and become an elongated trough of low pressure.  It will extend through the Plains states on Saturday intensifying a surface low pressure system and moving it north toward the Arctic.  At the same time a tropical system will be headed north from the Caribbean Sea into the Bahamas.

Thursday, October 18, 2012

Winter Outlook for 2012-13

The Climate Prediction Center released its early outlook for the upcoming winter this morning.  Much of the western U.S. will see warmer than normal temperatures while cooler than normal temperatures are expected for the Florida peninsula.  Equal chances of above or below normal temperatures are forecast for much of the East.

Much of the West will be dry particularly in the Pacific Northwest.  The Central Gulf region is expected to be wetter than normal.  This may help ease the drought in Georgia and South Carolina.

Click on either graphic for a larger version or go here for the temperature map and here for the precipitation map.  Image Credit: NOAA\CPC.

Sunday, October 14, 2012

Leaves Are Changing, But Later

By Climate Central

If it seems like autumn leaves are taking longer to change color, you’re not imagining things. Over the past 25 years, the onset of autumn has shifted. Fall now arrives two and a half weeks later in Columbia than it did in the early 1980s. This reflects the shift that's happening around the country, where leaves are staying on trees about 10.5 days later across the lower 48 states (see below).

The journal sourced is on the graphic.  Click on the image for a larger view.  Image Credit: Climate Central.

How do we know? Using satellite-based measurements of the Normalized Difference Vegetation Index (NDVI), which gauges leaf cover over wide areas, researchers at the Seoul National University in Korea found that the end of the growing season occurred progressively later over the course of their 26-year study. By noting the time of year changes in color occurred most rapidly, the researchers could track when fall in the lower 48 states started between 1982 and 2008.

Wednesday, October 10, 2012

The Global Weather Pattern Shifts

The previous post described how changes in the Arctic were causing changes in the weather and climate.  These changes extended down in the mid-latitudes where the impacts included cold, snowy winters.  However, the impacts of a warming earth do not end there.  Research shows that mankind is shifting the entire global atmospheric circulation.


Meteorologists have developed an idealized view of the global atmospheric circulation over the past century.  It has long been recognized that there is too much heat at the equator and too little at the poles.  The atmosphere acts like “the great equalizer “ by transporting heat from the tropics to the poles.  If the earth were not rotating, this would be a simple straight-forward transfer.

The situation is complicated by the fact that the earth does rotate on its axis.  This has given rise to the three-cell global circulation model.  The three cells from the tropics to the poles are named: Hadley, Ferrel, and Polar.  This model is pictured below with the resulting wind patterns.

The three-cell general circulation model of the atmosphere.  This is an idealized model based on observations.  Image credit: NASA.

The Hadley cell (also known as the tropical cell) extends from the equator to 30 degrees latitude.  Many of the world’s major deserts lie at the poleward extent of the Hadley cell where the air descends from upper levels.  This produces a persistent dry climate with little rainfall.  The North American Desert, Sahara, Australian Desert, and Kalahari Desert all are products of this circulation.

Tuesday, October 2, 2012

The Effects of Losing Arctic Sea Ice

A dramatic loss of Arctic sea ice occurred this year resulting in a record-shattering minimum in mid-September.  The implications were touched upon in a previous post.  However, it is recognized that the loss of Arctic sea ice is changing the ecology, geology, and meteorology of the region.

I will focus on the meteorology in this post.  The Arctic is warming at a rate that is twice that of the mid-latitudes in a phenomenon known as arctic amplification.  This faster warming is reducing the temperature gradient between the high and mid-latitudes which in turn is changing the dynamics of the jet stream.

Image Credit: NOAA.
The jet stream is a river of high velocity winds in the atmosphere.  It meanders generally from west to east around the globe.  The speed of the wind in the jet stream is usually stronger in the winter than in the summer, because the north-south temperature gradient is much stronger in winter.

A cross-section of the atmosphere shows how the lowest layer of the atmosphere, the troposphere, changes from the equator to the pole.  There are three circulation cells in the northern hemisphere and the jet streams are at the upper boundaries of the cells.  The jet stream helps to drive storm systems across the country so that knowledge of its future helps forecast future weather.